There is known from the prior art, particularly from EP Patent No. 0 762 243 in the name of the present Applicant, a timepiece, shown in FIG. 1, including a mechanical power source, formed by a barrel 1 which houses a manually or automatically wound spring 1a, the winding device not being shown here.
Barrel 1 is mechanically coupled to magnetized rotor 2a of an electric generator 2 via gear trains 3. Generator 2 includes at least a coil 2b which generates an alternating voltage Ug, when magnetized rotor 2a is driven in rotation, generating a magnetic field symbolized by means of an arrow and to which said at least one coil 2b is coupled.
The terminals of coil 2b (or coils) are connected to a rectifier 4 supplying at its output a rectified voltage Ua, for powering regulator circuit 6, which will be discussed hereinafter.
Analog display members for a time indication 5, typically a set of hands or any other conventional mechanical time display means, are mechanically coupled to the barrel via the gear trains 3 of the movement and they are connected in rotation to rotor 2a. The rotational speed of hands 5 is kept at a constant mean value owing to regulator circuit 6, which is for enslaving the generator frequency to a reference frequency, such that the speed of the hands corresponds to the speed required to obtain a correct time indication.
This regulator circuit 6 will not be described in detail here, since those skilled in the art can design such an enslaving device by referring to the description of the Swiss Patent Application No. 686 332 in the name of the present Applicant. However, in order to facilitate comprehension, the essential elements of this circuit and the operation thereof will be recalled here.
This regulator circuit 6 includes an oscillator 6a stabilized by a clock type quartz and a frequency divider 6b bringing the frequency of oscillator 6a to a frequency that can be used by a logic circuit 6c, which controls, via a control signal, a switching member 7, for example a transistor, for braking generator 2 in order to regulate its frequency to a reference frequency advantageously corresponding to a correct time indication by the time indication display members 5.
The timepiece according to this document also includes a power-reserve indicator 9. This device includes a counter 9a counting the successive braking signals 8 during a determined period of time by means of an additional frequency divider 9b. A memory 9c is connected at output to counter 9b so as to store the date counted during the determined time period, to the output of which a decoder 9d is connected, converting the stored data into a power-reserve display means control signal 9e including successive dashes which are illuminated or appear up to a point corresponding to the value of the measured or calculated variable, accomplished either by a colored strip, or a liquid crystal cell.
The solution recommended in EP Patent No. 0 762 243 has, however, the drawback of directly using the generator power to provide the power-reserve indication, which has the effect of increasing the total power drawn from the generator, i.e. the power necessary to provide the type indicator and the power necessary to provide the power-reserve indication. Thus, in most cases, the total power necessary represents an instantaneous power greater than the maximum capacity that the generator can provide, which may prove harmful, on the one hand, to the accuracy of the time indication and, on the other hand, to the actual supply of the power-reserve indication. And, at best, for those cases where the indications provided remain correct, the autonomy of the timepiece is greatly reduced.
There is also known from the prior art, particular from EP Patent No. 0 875 807 filed in the name of the present Applicant, a timepiece whose generator autonomy is Higher. Such a timepiece, shown in FIG. 2, includes, in addition to known elements, which have the same reference numerals and were already described with reference to FIG. 1, a storage device 10 for storing and returning the electrical energy formed by a part of the electrical energy of generator 2. This storage device 10 connected to the terminals of rectifier 4 includes a conventional accumulator 10a. 
When the barrel spring 1a is completely let down and rotor 2a of generator 2 is not rotating, voltage Ug is obviously zero. If, moreover, accumulator 10a of storage device 10 is discharged, voltage Ua is also zero, or in any case insufficient for the timepiece to operate. If barrel spring 1a is then wound, a moment is reached at which rotor 2a starts to rotate, and where voltages Ug and Ua start to increase.
Accumulator 10a is completely, or at least almost completely, discharged when the timepiece is stopped. When rotor 2a starts to rotate and voltage Ua reaches a sufficient value, accumulator 10a starts to charge by absorbing part of the electrical energy provided by generator 2. This excess of electrical energy is of course supplied by the barrel spring 1a and originates from the conversion by generator 2 of at least a part of the spring's mechanical energy.
If the motor torque provided by barrel spring 1a becomes less than the operating threshold torque of the timepiece, the electrical energy produced by generator 2 becomes insufficient to power the various circuits of regulator circuit 6 correctly. But, accumulator 10a is then at least partially charged, such that storage device 10 keeps voltage Ua at a value such that the components of regulator circuit 6 operate properly. The electrical energy necessary for such operation is then supplied, at least partially, by accumulator 10a. 
Thus, the autonomy of this timepiece, which includes a storage device 10 capable of storing, in the form of electrical energy, a part of the mechanical energy contained in its barrel spring, is increased owing to means which enables this electrical energy to be used for operating the timepiece after the barrel spring is no longer sufficiently wound.
Nonetheless, a timepiece as described in EP Patent No. 0 875 807 only enables the instantaneous excess power to be stored compared to that necessary to make the timepiece operate properly. Thus, the use of this excess of instantaneous power to provide an additional indication, like for example the power reserve, would have the same drawbacks as those described in conjunction with EP Patent No. 0 762 243, namely directly using the power drawn from the generator, with the effect of greatly reducing the timepiece's autonomy, which is contrary to the desired objective.